Technologies, such as carrier aggregation and multi-input multi-output (MIMO), have been introduced in recent years for the purpose of improving throughput in a wireless communication system. Carrier aggregation refers to a technology in which a base station device and a wireless terminal device communicate with each other using a plurality of carriers different in frequency. MIMO refers to a technology in which a transmitting side transmits different pieces of data from a plurality of transmitting antennas, and a receiving side derives pieces of data transmitted from respective transmitting antennas from signals received by a plurality of receiving antennas.
With the introduction of the technologies, various signals different in frequency are transmitted within and outside wireless communication devices, such as a base station device and a wireless terminal device. If a distortion source, such as metal, is present on a transmission channel for such signals, intermodulation between signals different in frequency causes passive intermodulation (PIM). That is, an intermodulation signal having a frequency which is the sum of or the difference between multiples of the frequencies of the signals is generated at the distortion source. If the frequency of an intermodulation signal is included in a reception frequency band of a wireless communication device, the intermodulation signal hampers demodulation and decoding of a reception signal to lower reception quality.
To curb a reduction in reception quality due to such an intermodulation signal, for example, the idea of approximately regenerating an intermodulation signal resulting from intermodulation between a transmission signal transmitted from a wireless communication device and an interference signal transmitted from a different wireless communication device and canceling the intermodulation signal included in a reception signal is under consideration.
An intermodulation signal (hereinafter referred to as a PIM signal) may be regenerated by computation. A PIM signal which is regenerated by computation is a replica of a PIM signal which is generated due to a plurality of transmission signals. A signal obtained by inverting the phase of the PIM signal is added to a reception signal, thereby canceling the PIM signal in the reception signal. Accurate estimation of when a PIM signal arrives is important in canceling the PIM signal.
International Publication Pamphlets Nos. WO 2014/083361 and WO 2010/082431 are examples of related art.